Root exudate components change litter decomposition in a simulated rhizosphere depending on temperature

The release of root exudates into the rhizosphere is known to enhance soil biological activity and alter microbial community structure. To assess whether root exudates also stimulated litter decomposition, in a rhizosphere model system we continuously injected solutions of glucose, malate or glutamate through porous Rhizon((R)) supercript stop soil solution samplers into the soil at rhizosphere concentrations. The effect of these substances on the decomposition of C-14-labelled Lolium perenne shoot residues present in the soil was evaluated by monitoring (CO2)-C-14 evolution at either 15 degrees C or 25 degrees C. The incorporation of the C-14 into the microbial biomass and appearance in the dissolved organic matter (DOM) pool was estimated after 32 d incubation. The presence of malate and glutamate increased the mineralization of L. perenne residues by approximately 20% relative to the soil without their addition at 15 degrees C, however, no significant effects on residue decomposition were observed at 25 degrees C. The incorporation of the C-14-label into the microbial biomass and DOM pool was not affected by the addition of either glucose, malate or glutamate. Although nearly the same amount of L. perenne residues were mineralized at either temperature after 32 d, less C-14 was recovered in the microbial biomass and DOM pools at 25 degrees C compared to 15 degrees C. Alongside other results, this suggests that the rate of microbial turnover is greater at 25 degrees C compared to 15 degrees C. We conclude that the addition of labile root exudate components to the rhizosphere induced a small but significant increase on litter decomposition but that the magnitude of this effect was regulated by temperature.